What happens to Ontrack?

using like rtcPeerConnection = new RTCPeerConnection, rtcPeerConnection.ontrack doesnt work anymore?

im using react-native-webrtc = 1.75.3

If you check over here work on Unified Plan support is getting closer to being completed.
That will bring transceiver support along with the latest track handling and events.

if thats is in under progress, i dont have what to do, thanks

It is indeed in progress and due to be released in the future once stable.
You could clone this branch and test things before then.